Effect of Anderson magnetic impurities on superconductivity

Abstract

For the purpose of clarifying the Kondo effect in superconductors, in particular, at lower temperatures than a characteristic temperature $T_K$, a perturbation calculation is performed within the Anderson model. In a microscopic Fermi-liquid theory which accurately describes the low-energy excitations, we consider the transition temperature $T_c$ and the jump in the specific heat $\Delta C$ of the alloys. The energy dependence of the magnetic scattering generally leads to a finite tail in the concentration dependence of $T_c$, which suggests the existence of the third transition back to a superconducting state at a low temperature in superconducting alloys showing a "reentrance" phenomenon. Alloys with high Kondo temperatures are found to be well described by a nonmagnetic Hartree-Fock solution with renormalized parameters. In addition, expansion formulas for the four-vertex parts of the electron scattering are derived near the Fermi surface.